This application is based on Japanese Patent Applications No. 2000-056295 filed Mar. 1, 2000 and No. 2000-183596 filed Jun. 19, 2000, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a braking pressure source device for an automotive vehicle, and more particularly to a braking pressure source device including a master cylinder wherein a pressurizing piston partially defines a pressurizing chamber and a back-pressure chamber on opposite sides thereof so that the pressure in the back-pressure chamber acts on the pressurizing piston.
2. Discussion of Related Art
Japanese Patent Application No. 10-364575 filed by the assignee of this invention but not laid open at the time the present invention was made discloses one type of a braking pressure source device which includes a master cylinder wherein a pressurizing piston partially defines a back-pressure chamber on a rear side thereof so that a back pressure in the back-pressure chamber acts on the pressurizing piston in an advancing direction of the pressurizing piston. In this type of braking pressure source device, the pressurizing piston is fluid-tightly and slidably received in the cylinder housing of the master cylinder, and cooperates with the cylinder housing to define a pressurizing chamber and the back-pressure chamber on respective front and rear sides thereof, and an input rod is formed integrally with the pressurizing piston fluid-tightly and slidably extends outward through the rear end wall of the cylinder housing which partially defines the back-pressure chamber. In operation, a working fluid in the pressurizing chamber is pressurized by an advancing movement of the pressurizing piston on the basis of a brake operating force acting on a manually operable brake operating member. Further, the pressurizing chamber and the back-pressure chamber are connected to each other through a communication passage, in which is provided a normally closed solenoid-operated shut-off valve.
In the braking pressure source device described above, the back-pressure chamber is supplied with the working fluid pressurized by a power-operated hydraulic pressure source, which includes a pump and an accumulator. The pressure of the pressurized fluid delivered from the pump or accumulator is controlled by a pressure control valve device, and the fluid having the thus controlled pressure is supplied to the back-pressure chamber. The pressurizing piston receives a force based on the brake operating force and a force based on the back pressure, namely, the pressure of the pressurized fluid supplied to the back-pressure chamber, so that the fluid in the pressurizing chamber is pressurized to a pressure higher than a level that is established by only the brake operating force. Thus, the brake operating force is boosted by the pressurized fluid in the back-pressure chamber. When the power-operated hydraulic pressure source becomes defective, for instance, when the accumulator suffers from a fluid leakage preventing a supply of the pressurized fluid from the power-operated hydraulic pressure source to the back-pressure chamber, the back-pressure chamber is disconnected from the power-operated hydraulic pressure source, and the solenoid-operated shut-off valve provided in the communication passage is opened, permitting a flow of the fluid from the back-pressure chamber into the pressurizing chamber. When the pressurizing piston is advanced in this state, the fluid pressurized in the pressurizing chamber is fed into the back-pressure chamber, so that the effective surface area in transverse cross section or effective diameter of the pressurizing piston is reduced to that of the input rod. Accordingly, the pressure in the pressurizing chamber (hereinafter referred to as xe2x80x9cmaster cylinder pressurexe2x80x9d where appropriate) corresponding to a given amount of brake operating force acting on the input rod is made higher when the pressurizing chamber and the back-pressure chambers are communicated with each other than when these chambers are not communicated with each other. Thus, the master cylinder pressure generated when the pressurized fluid cannot be delivered from the power-operated hydraulic pressure source to the back-pressure chamber is as high as that when the pressurized fluid is delivered to the back-pressure chamber.
It is therefore an object of the present invention to provide a braking pressure source device including a master cylinder in which a pressurizing chamber and a back-pressure chamber formed on the respective front and rear sides of a pressurizing piston are connected to each other through a communication passage provided with a communication control valve device including a solenoid-operated valve, and wherein the communication control valve device is controlled in a manner different from that in the braking pressure source device described in the above-identified Japanese Patent Application.
The above object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combination thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking pressure source device provided in a braking system for an automotive vehicle, the braking system including a brake operating member manually operable with a brake operating force applied thereto, the braking pressure source device comprising:
a master cylinder including a cylinder housing, a pressurizing piston fluid-tightly and slidably received in the cylinder housing and cooperating with the cylinder housing to define a pressurizing chamber and a back-pressure chamber on a front and a rear side of the pressurizing piston, and an input rod which fluid-tightly and slidably extends through a rear end wall of the cylinder housing, the pressurizing piston being advanced by the brake operating force of the brake operating member transmitted thereto through the input rod, to pressurize a working fluid in the pressurizing chamber;
means for defining a communication passage for communication between the pressurizing chamber and the back-pressure chamber;
a first control valve device disposed in the communication passage for controlling the communication between the pressurizing and back-pressure chambers through the communication passage; and
a first control valve control device for controlling the first control valve device,
and wherein the first control valve control device controls the first control valve device on the basis of at least one of an operating state of the brake operating member, a running state of the automotive vehicle and a state of a road surface on which the automotive vehicle is running.
The operating state of the brake operating member includes, for example, an operating force and an operating stroke of the brake operating member, and rates of change of these operating force and stroke. The operating force can be directly detected, or indirectly detected by detecting a physical quantity which changes with the operating force of the brake operating member, such as a fluid pressure in the pressurizing chamber. The state of the road surface includes, for instance, a friction coefficient and a gradient of the road surface, and the presence or absence of recessed, raised and/or stepped areas in the road surface. The running condition of the vehicle includes, for instance, slipping states of the vehicle wheels, and running or turning stability, speed and acceleration of the vehicle. The running or turning stability of the vehicle may be represented by a difference between a desired yaw rate determined by an angle of a steering wheel of the vehicle and the vehicle running speed, and an actual yaw rate detected by a yaw rate sensor, or represented by a rate of change of the above-indicated difference.
The brake operating member may be brake pedal operable by foot by the vehicle operator, or a brake lever operable by hand by the vehicle operator.
When the first control valve device is controlled to effect fluid communication between the pressurizing and back-pressure chambers through the communication passage, the pressurized fluid is delivered from the pressurizing chamber to the back-pressure chamber, so that the fluid pressure in the back-pressure chamber is increased. The first control valve device may be principally constituted by a solenoid-operated shut-off valve or a solenoid-operated pressure control valve. In the former case, the solenoid-operated shut-off valve is opened to reduce the effective diameter of the pressurizing piston to that of the input rod of the master cylinder, so that the fluid pressure in the pressurizing chamber (master cylinder pressure) corresponding to a given value of the operating force of the brake operating member (brake operating force) is made higher than when the solenoid-operated shut-off valve is in the closed state disconnecting the pressurizing and back-pressure chambers from each other. In the latter case, the solenoid-operated pressure control valve may be a linear solenoid valve whose amount of opening is linearly variable by continuously controlling the amount of electric current applied thereto. In this case, the relationship between the brake operating force and the master cylinder pressure can be controlled as desired. That is, by controlling the solenoid-operated pressure control valve, a back pressure is generated in the back-pressure chamber, so that the master cylinder pressure is increased to a sum of the fluid pressure generated in the pressurizing chamber by only the brake operating force and the back pressure generated in the back-pressure chamber. The back pressure generated in the back-pressure chamber can be controlled as desired by controlling the amount of electric current to be applied to the solenoid-operated pressure control valve, so that the master cylinder pressure in the pressurizing chamber can be controlled as needed. In this case, too, the effective diameter of the pressurizing piston is partially reduced owing to partial communication between the pressurizing and back-pressure chamber. This reduction of the effective diameter of the pressurizing piston may be considered to be xe2x80x9cpartial reductionxe2x80x9d or xe2x80x9cincomplete reductionxe2x80x9d of the effective diameter, as distinguished from xe2x80x9ccomplete reductionxe2x80x9d of the effective diameter which is effected when the two chambers are fully communicated with each other.
In the present braking pressure source device, the relationship between the brake operating force and the master cylinder pressure can be changed as needed, without the provision of a power-operated hydraulic pressure source including a power-operated pump adapted to deliver a pressurized fluid to the back-pressure chamber. Accordingly, the present braking pressure source device is available at a relatively low cost. By controlling the first control valve device on the basis of at least one of the operating state of the brake operating member, the state of the road surface and the running condition of the vehicle, it is possible to facilitate an anti-lock braking pressure control for slipping wheels, so as to maximize the overall vehicle braking force, possible to facilitate the braking operation during running of the vehicle on a road surface having a relatively low friction coefficient, and possible to perform various controls of the vehicle braking force upon detection of a requirement for an abrupt or emergency brake application to the vehicle, upon detection of a defect of a booster or a braking sub-system associated with a vehicle wheel brake, or upon detection that the boosting limit of the booster has been reached.
However, the principle of the present invention does not inhibit the provision of a power-operated hydraulic pressure source for supplying the back-pressure chamber with a pressurized fluid. Where the power-operated hydraulic pressure source is provided, this power-operated hydraulic pressure source is used to supply the back-pressure chamber with the pressurized fluid as long as the power-operated hydraulic pressure source is normal, and the first control valve device is controlled for fluid communication between the pressurizing chamber and the back-pressure chamber where the power-operated hydraulic pressure source is defective. Further, the first control valve device may be controlled for fluid communication between the pressurizing and back-pressure chambers, while the power-operated hydraulic pressure source is normal. Where the braking system has mutually independent two or more braking sub-systems, for instance, two braking sub-systems, the power-operated hydraulic pressure source may be operated for operating a normally operable one of the two braking sub-systems when the other braking sub-system is defective. If the vehicle operator""s vehicle braking effect cannot be obtained even when the pressure of the pressurized fluid delivered from the power-operated hydraulic pressure source has reached the upper limit, the first control valve device is controlled for fluid communication between the pressurizing and back-pressure chambers to reduce the effective diameter of the pressurizing piston.
(2) A braking pressure source device according to the above mode (1), further comprising:
a reservoir for storing the working fluid at a pressure substantially equal to an atmospheric pressure;
a connecting passage connecting the reservoir and the back-pressure chamber; and
a check valve disposed in the connecting passage which permits a flow of the fluid in a first direction from the reservoir toward the back-pressure chamber and inhibits a flow of the fluid in a second direction opposite to the first direction.
In the braking pressure source device according to the above mode (2), the fluid is delivered from the reservoir into the back-pressure chamber when the pressurizing piston is advanced while the back-pressure chamber is disconnected from the pressurizing chamber. In other words, a supply of the fluid from the reservoir to the back-pressure chamber permits an advancing movement of the pressurizing piston. Accordingly, it is possible to easily control the relationship between the master cylinder pressure and the brake operating force, while preventing the back-pressure in the back-pressure chamber from being lowered below the atmospheric level.
(3) A braking pressure source device according to the above mode (1) or (2), wherein the first control valve device includes a solenoid-operated pressure control valve capable of controlling a fluid pressure difference across the solenoid-operated pressure control valve, according to an amount of electric current applied thereto, and the first control valve control device includes a current control portion operable to control the amount of electric current to be applied to the solenoid-operated pressure control valve on the basis of at least one of the operating state of the brake operating member, the running state of the automotive vehicle and the state of the road surface.
In the braking pressure source device according to the above mode (3), the relationship between the master cylinder pressure and the brake operating force can be controlled as desired.
The solenoid-operated pressure control valve may be a normally open valve which is open for fluid communication between the pressurizing chamber and the back-pressure chamber while no electric current is applied to its solenoid coil, and is closed when an electric current is applied to the solenoid coil. Alternatively, the solenoid-operated pressure control valve may be a normally closed valve which is closed for disconnecting the pressurizing and back-pressure chambers while no electric is applied to the solenoid coil, and is opened for fluid communication between the chambers when an electric current is applied to the solenoid coil.
The first control valve device may be principally constituted by a solenoid-operated shut-off valve, which may be a normally open valve or a normally closed valve. In either case, it is possible to control the relationship between the master cylinder pressure and the brake operating force by controlling the duty ratio of the solenoid coil. However, the accuracy of control of the above-indicated relationship is higher where the first control valve device is principally constituted by the solenoid-operated pressure control valve than where the first control valve device is principally constituted by the solenoid-operated shut-off valve. The solenoid-operated pressure control valve may be arranged such that the fluid pressure difference across the valve acts in the valve-opening direction or in the valve-closing direction.
(4) A braking pressure source device according to any one of the above modes (1)-(3), further comprising flow restricting provided in the communication passage.
Where the first control valve device is principally constituted by a solenoid-operated shut-off, valve, the flow restricting means is a flow restrictor provided separately from the shut-off valve. Where the first control valve device is principally constituted by a solenoid-operated pressure control valve, the flow restricting means may be a separate flow restrictor, or alternatively the solenoid-operated pressure control valve may incorporate the flow restricting means. In the latter case, the solenoid-operated pressure control valve is constructed such that the amount of opening is controlled with a change in the amount of electric current to be applied to its solenoid coil, so that the rate of flow of the pressurized fluid from the pressurizing chamber to the back-pressure chamber is controlled as the amount of electric current is changed.
The flow restricting means provided in the communication passage makes it possible to prevent a rapid flow of the pressurizing fluid from the pressurizing chamber to the back-pressure chamber when the first control valve device is opened to effect the fluid communication between the two chambers. Accordingly, the flow restricting means facilitates the control of the master cylinder pressure, and is effective to minimize an influence of the fluid flow between the chambers on the brake operating member, which influence is unexpected to the vehicle operator.
(5) A braking pressure source device according to any one of the above modes (1)-(4), further comprising:
a reservoir for storing the working fluid at a pressure substantially equal to an atmospheric pressure;
a connecting passage connecting the reservoir and the back-pressure chamber; and
a second control valve device disposed in the connecting passage and capable of controlling a fluid pressure difference across the second control valve device, according to an amount of electric current applied thereto.
The second control valve device may be principally constituted by a solenoid-operated shut-off valve or a solenoid-operated pressure control valve.
Like the solenoid-operated pressure control valve of the first control valve device, the solenoid-operated pressure control valve of the second control valve device may be a normally open valve or a normally closed valve. Whether the solenoid-operated pressure control valve of the second control valve device is the normally open valve or the normally closed valve is preferably determined depending upon the construction of the solenoid-operated pressure control valve or shut-off valve of the first control valve device. In either case, the solenoid-operated pressure control valve of the second control valve device facilitates the control of the back pressure in the back-pressure chamber, by controlling the rate of flow of the working fluid from the back-pressure chamber to the reservoir with a change in the amount of electric current applied thereto. Where the second control valve device is principally constituted by the solenoid-operated shut-off valve, this shut-off valve may be simply opened and closed, or the duty ratio of its solenoid coil may be controlled. The shut-off valve of the second control valve device may also be either a normally open valve or a normally closed valve.
In the braking pressure source device according to the above mode (5), the second control valve device provided in the connecting passage further facilitates the control of the master cylinder pressure in relation to the brake operating force. (6) A braking pressure source device according to any one of the above modes (1)-(5), wherein the braking system includes a front wheel brake for braking a front wheel of the automotive vehicle, and a rear wheel brake for braking a rear wheel of the automotive vehicle, and the master cylinder includes a first pressurizing piston and a second pressurizing piston which are disposed in series with each other in the cylinder housing and cooperate with the cylinder housing to define a first pressurizing chamber and a second pressurizing chamber, respectively, on front sides of the first and second pressurizing pistons, respectively, one of the first and second pressurizing chambers being connected to the front wheel brake while the other of the first and second pressurizing chambers being connected to the rear wheel brake, and wherein the other pressurizing chamber is connected to the back-pressure chamber through the communication passage.
In the braking pressure source device according to the above mode (6), the first control valve device is controlled to effect the fluid communication between the above-indicated other pressurizing chamber and the back-pressure chamber through the communication passage, when the front braking sub-system including the front brake is defective, for instance. In this case, the fluid pressure in the above-indicated other pressurizing chamber is increased to effectively reduce the amount of reduction of the total vehicle braking force when the front braking sub-system is defective.
In a braking system for an automotive vehicle, the front wheel brake generally has a larger braking capacity than the rear wheel brake. Accordingly, the total vehicle braking capacity is considerably reduced when the front braking sub-system is defective. In the braking pressure source device according to the above mode (6), however, the pressurizing chamber connected to the rear wheel brake is communicated with the back-pressure chamber to increase the fluid pressure in this pressurizing chamber of the master cylinder, so that the reduction of the total vehicle braking force when the front braking sub-system is defective can be effectively minimized.
(7) A braking pressure source device according to the above mode (6), wherein the front wheel brake has a front wheel brake cylinder for braking the front wheel, and the rear wheel brake has a rear wheel brake cylinder for braking the rear wheel, the first control valve control device including:
a front-wheel anti-lock control detecting portion for detecting initiation of an anti-lock braking pressure control for controlling the front wheel brake cylinder so as to prevent an excessive tendency of slipping of the front wheel on a road surface which takes place, during an operation of the front wheel brake, due to a fluid pressure in the front wheel brake cylinder which is excessively high in relation to a friction coefficient of the road surface; and
a communication control portion operable upon detection by the front-wheel anti-lock control detecting portion of the initiation of the anti-lock braking pressure control, to command the first control valve device to effect the fluid communication between the above-indicated other pressurizing chamber and the back-pressure chamber through the communication passage.
When the anti-lock braking pressure control has been initiated for the front wheel brake cylinder, the above-indicated other pressurizing chamber connected to the rear wheel brake is communicated with the back-pressure chamber through the communication passage, to increase the fluid pressure in the above-indicated other pressurizing chamber. The fluid pressure in the above-indicated other pressurizing chamber is increased since the above-indicated one pressurizing chamber has already been disconnected from the front wheel brake cylinder, so that the fluid pressure in the rear wheel brake cylinder (rear wheel brake cylinder pressure) is increased, whereby the total vehicle braking force is accordingly increased. If the rear wheel has an excessive slipping tendency in relation to the friction coefficient of the road surface as a result of an increase in the rear wheel brake cylinder pressure, an anti-lock braking pressure control is initiated for the rear wheel brake cylinder. The present arrangement is particularly effective in a braking system of the type which is adapted to initiate the anti-lock braking pressure control for the front wheel before the anti-lock braking pressure control for the rear wheel. However, the present arrangement may be effective also in a braking system of the type not adapted as described above, since this type of braking system may initiate the anti-lock braking pressure control for the front wheel brake cylinder before the anti-lock braking pressure control for the rear wheel brake cylinder, when the friction coefficient of an area of the road surface on which the front wheel lies is temporarily considerably lower than that of an area of the road surface on which the rear wheel lies.
(8) A braking pressure source device according to any one of the above modes (1)-(7), wherein the braking system includes a wheel brake having a wheel brake cylinder for braking a wheel of the automotive vehicle, and the first control valve control device includes:
an anti-lock control detecting portion for detecting initiation of an anti-lock braking pressure control for controlling the wheel brake cylinder so as to prevent an excessive tendency of slipping of the wheel on a road surface which takes place, during an operation of the wheel brake, due to a fluid pressure in the wheel brake cylinder which is excessively high in relation to a friction coefficient of the road surface; and
a communication control portion operable upon detection by the anti-lock control detecting portion of the initiation of the anti-lock braking pressure control, to command the first control valve device to effect the fluid communication between the pressurizing chamber and the back-pressure chamber through the communication passage.
When the pressurizing chamber is communicated with the back-pressure chamber through the communication passage, the rate of increase of the fluid pressure in the pressurizing chamber (master cylinder pressure) with an increase in the operating stroke of the brake operating member is reduced, so that the master cylinder pressure can be easily controlled. Where the vehicle is braked on a frozen road surface, for example, the anti-lock braking control for the wheel brake cylinder is initiated while the master cylinder pressure is comparatively low, so that the amount of change of the operating stroke of the brake operating member is considerably reduced, resulting in hard operating feel of the brake operating member, making it difficult to intricately control the operating force of the brake operating member. The road surface is frozen as a result of freezing of water on the road surface into a layer of ice, or as a result of compaction of a layer of snow on the road surface by tires of vehicles running on the layer of snow. In the latter case, the frozen road surface may be a mirror surface having a considerably low friction coefficient, so that the vehicle operator has considerable difficulty to intricately manipulate the brake operating member during brake application to the vehicle running on such a mirror surface. The present braking pressure source device is effective to reduce this difficulty, since the fluid communication between the pressurizing and back-pressure chambers causes an increase in the operating stroke of the brake operating member to establish a given level of the master cylinder pressure.
When the pressurizing chamber is communicated with the back-pressure chamber to deliver the pressurized fluid from the pressurizing chamber to the back-pressure chamber, the total amount of the fluid discharged from the pressurizing chamber is made larger than when the pressurizing and back-pressure chambers are not communicated with each other. Accordingly, the operating stroke of the brake operating member is made larger when the two chambers are communicated with each other. The amount of increase of the operating stroke of the brake operating member is maximized when the pressurizing and back-pressure chambers are held in communication with each other so as to reduce the effective diameter of the pressurizing piston. In this case, the operating force of the brake operating member can be controlled with utmost ease.
(9) A braking pressure source device according to any one of the above modes (1)-(8), wherein said first control valve control device includes:
an abrupt-brake-application detecting portion operable to detect a requirement for an abrupt brake application to the automotive vehicle; and
a communication control portion operable upon detection by said abrupt-brake-application detecting portion of said requirement for said abrupt brake application, to command said first control valve to effect the fluid communication between said pressurizing chamber and the back-pressure chamber through the communication passage.
When an abrupt brake application to the vehicle is required, it is desirable to maximize the master cylinder pressure. The present braking pressure source device is capable of meeting this desire.
The communication control portion provided in the present braking pressure source device is arranged to hold the pressurizing chamber and the back-pressure chamber in communication with each other, to reduce the effective diameter of the pressurizing piston. In principle, the communication control portion is arranged to maintain the fluid communication between the two chambers. However, the communication control portion may be adapted to hold the two chambers in communication with each other during an initial period of the abrupt brake application, until the master cylinder pressure has been increased to a predetermined level. In this case, the communication control portion is adapted to command the control of the first control valve device to initiate the control of the fluid pressure difference across the first control valve device, when the master cylinder pressure has been increased to the predetermined level, for controlling the back pressure in the back-pressure chamber so that the master cylinder pressure after the master cylinder pressure has been increased to the predetermined level is increased at a lower rate than while the pressurizing and back-pressure chambers were held in communication with each other.
(10) A braking pressure source device according to the above mode (9), wherein the communication control portion commands the first control valve device to effect the fluid communication between the pressurizing chamber and the back-pressure chamber when a rate of increase of the operating force of the brake operating member has been reduced below a predetermined threshold after the requirement for the abrupt brake application is detected by the abrupt-brake-application detecting portion.
If the pressurizing and back-pressure chambers are communicated with each other when the requirement for the abrupt brake application is detected by the abrupt-brake-application detecting portion, the operating force of the brake operating member is considerably increased. In the braking pressure source device according to the above mode (10), the two chambers are communicated with each other through the communication passage when the rate of increase of the brake operating force has been reduced below the predetermined threshold. This arrangement permits an increase of the master cylinder pressure while preventing a considerable increase of the brake operating stroke.
The predetermined threshold of the rate of increase of the brake operating force is determined such that the master cylinder pressure is increased to a level close to the level desired by the vehicle operator when the rate of increase of the brake operating force has been reduced below the threshold, that is, such that when the rate of increase has been reduced below the threshold the vehicle operator has operated the brake operating member to a position at which the master cylinder pressure is close to the level desired by the vehicle operator. When the pressurizing and back-pressure chambers are communicated with each other in this state, the amount of subsequent increase of the brake operating stroke is not so large.
(11) A braking pressure source device according to any one of the above modes (1)-(10), wherein the first control valve control device includes:
a low-friction-coefficient detecting portion operable to detect that a friction coefficient of a road surface on which the automotive vehicle is running is lower than a predetermined threshold; and
a communication control portion operable upon when the low-friction-coefficient detecting portion has detected that the friction coefficient is lower than the predetermined threshold, to command the first control valve device to effect the fluid communication between the pressurizing chamber and the back-pressure chamber through the communication passage.
When the vehicle is braked on a road surface having a low friction coefficient, the operating force of the brake operating member is required to be intricately controlled. The braking pressure source device according to the above mode (11) is capable of easily satisfying this requirement. Namely, the fluid communication between the pressurizing and back-pressure chamber causes a decrease in the rate of increase of the master cylinder pressure with an increase in the brake operating force.
(12) A braking pressure source device according to any one of the above modes (1)-(11), further comprising a booster for boosting the brake operating force and transmitting the boosted brake operating force to the input rod of the master cylinder, and wherein the first control valve control device includes:
a booster defect detecting portion operable to detect a defect of the booster; and
a communication control portion operable upon detection of the defect of the booster by the booster defect detecting portion, to command the first control valve device to effect the fluid communication between the pressurizing chamber and the back-pressure chamber through the communication passage.
In the braking pressure source device according to the above mode (12), the pressurizing and back-pressure chambers are communicated with each other to reduce the effective diameter of the pressurizing piston for thereby increasing the master cylinder pressure, when the booster is defective, that is, when the booster is not capable of boosting the brake operating force. Accordingly, the amount of reduction of the vehicle braking force due to the defect of the booster can be minimized.
(13) A braking pressure source device according to any one of the above modes (1)-(12), further comprising a booster for boosting the brake operating force and transmitting the boosted brake operating force to the input rod of the master cylinder, and wherein the first control valve control device includes:
a boosting limit detecting portion operable to detect that a boosting limit of the booster has been reached; and
a communication control portion operable upon detection by the boosting limit detecting portion that the boosting limit of the booster has been reached, to command the first control valve device to start controlling a fluid pressure difference across the first control valve device.
In the braking pressure source device according to the above mode (13), the back pressure in the back-pressure chamber is controlled after the boosting limit of the booster has been reached, so that the master cylinder pressure can be increased at the same rate as before the boosting limit has been reached.
(14) A braking pressure source device according to any one of the above modes (1)-(13), wherein the first control valve control device controls the first control valve device on the basis of at least one of the brake operating force and a pressure of the fluid in the pressurizing chamber, and a rate of change of each of the above-indicated at least one of the brake operating force and the pressure.
The relationship between the brake operating force and the master cylinder pressure (pressure in the pressurizing chamber) can be further intricately controlled, by controlling the first control valve device on the basis of not only at least one of the brake operating force and the master cylinder pressure, but also a rate of change of the brake operating force and/or a rate of change of the master cylinder pressure. The braking pressure source device according to the above mode (10) is one example of the braking pressure source device according to the above mode (14).
(15) A braking pressure source device according to any one of the above modes (1)-(14), wherein the first control valve control device controls the first control valve device on the basis of at least one of the brake operating force and a pressure of the fluid in the pressurizing chamber, and a time which has passed after a moment of detection of: (a) initiation of an anti-lock braking pressure control for controlling a front wheel brake cylinder of the braking system so as to prevent an excessive tendency of slipping of a front wheel of the automotive vehicle on a road surface on which the automotive vehicle is running; (b) initiation of an anti-lock braking pressure control for controlling a wheel brake cylinder of the braking system so as to prevent an excessive tendency of slipping of a wheel of the automotive vehicle on the road surface; (c) a requirement for an abrupt brake application to the automotive vehicle; (d) reduction of a friction coefficient of the road surface below a predetermined threshold; (e) a defect of a booster capable of boosting the brake operating force and transmitting the boosted brake operating force to the input rod of the master cylinder; and (f) a state in which a boosting limit of the booster has been reached.
In the braking pressure source device according to the above mode (15), the first control valve control device may be adapted to command the first control valve device to effect the fluid communication between the pressurizing and back-pressure chambers through the communication passage, when the predetermined time has passed after the moment of detection of any one of the above-indicated states or events. This arrangement permits the effective utilization of the back pressure in the back-pressure chamber while reducing an increase of the brake operating stroke. The predetermined time may be a fixed time, or may be changed depending upon the rate of increase of the brake operating force or the master cylinder pressure upon, before or after detection of any one of the above-indicated states or events.
For instance, the predetermined time after the moment of detection of the requirement for an abrupt brake application to the vehicle is reduced with an increase in the rate of increase of the brake operating force or master cylinder pressure, since the rate of increase of the brake operating force or master cylinder pressure is relatively high at the moment when the abrupt brake application is required. This arrangement permits an increase of the master cylinder pressure without a delay, while reducing an increase of the brake operating stroke.
(16) A braking pressure source device according to any one of the above modes (1)-(15), further comprising a brake operating force boosting device operable to boost the brake operating force of the brake operating member and transmitting the boosted brake operating force to the pressurizing piston.
(17) A braking pressure source device according to the above mode (16), wherein the brake operating force boosting device includes a boosting ratio changing portion operable to change a ratio of boosting of the brake operating force, depending upon an operating stroke of the brake operating member.
The master cylinder pressure can be easily controlled to a level close to the desired level, by maximizing the boosting ratio of the brake operating force boosting device when the master cylinder pressure is at a predetermined level, and then reducing the boosting ratio. This arrangement assures a relatively hard operating feel of the brake operating member as felt by the vehicle operator after the boosting ratio is reduced. Further, the present arrangement is effective to reduce the maximum brake operating stroke. In addition, the master cylinder pressure can be increased in various manners, by changing the boosting ratio of the brake operating force changing portion in various patterns, in suitable combinations with the moment and manner at or in which the pressurizing chamber and the back-pressure chamber are communicated with each other by the first control valve device.
(18) A braking pressure source device according to the above mode (5), further comprising a first diagnosing portion operable to diagnose at least one of the first control valve device and the second control valve device, during reduction of the brake operating force while the automotive vehicle is stationary.
The first and second control valve devices disposed in the communication passage and the connecting passage, respectively, can be diagnosed without operator""s recognition of the diagnosis, if the diagnosis is effected while the vehicle is stationary. If the diagnosis is effected while the brake operating force is being reduced, the control valve devices can be diagnosed for sticking of their valve members in the open state (a defect that the control valve devices cannot be closed). Where the first control valve device in the communication passage is open while the second control valve device in the connecting passage is stuck in its open state, the pressurizing chamber is held in communication with the reservoir. Therefore, it is desirable not to open the first control valve device in the communication passage while the second control valve device in the connecting passage is stuck in the open state. In this respect, it is particularly desirable to diagnose the second control valve device for sticking of its valve member in the open state.
(19) A braking pressure source device according to any one of the above modes (1)-(18), further comprising a second diagnosing portion operable while the automotive vehicle is stationary, to command the first control valve device to effect the fluid communication between the pressuring chamber and the back-pressure chamber through the communication passage, and diagnosing the braking pressure source device on the basis of an operating state of the braking pressure source device after the first control valve device is commanded to effect the fluid communication.
The braking pressure source device is operated with an operation of the brake operating member, or without an operation of the brake operating member. In the latter case, the braking pressure source device is operated, for example, with an operation of a power-operated hydraulic pressure source as provided according to the mode (39) of this invention (which will be described), without an operation of the brake operating member. In this case, the pressurizing piston is advanced as a pressurized fluid is delivered from the power-operated hydraulic pressure source to the back-pressure chamber, and the fluid in the pressurizing chamber is pressurized. Alternatively, the pressurized fluid is delivered from the power-operated hydraulic pressure source to the pressurizing chamber through the communication passage and the first control valve device placed in the open state, so that the braking pressure source device is operated without an operation of the brake operating member.
Where the breaking pressure source device is operated with an operation of the brake operating member, the first control valve device is controlled to effect the fluid communication through the pressurizing and back-pressure chambers through the communication passage. If the master cylinder pressure can be increased to a level which corresponds to the specific operating amount (operating force or stroke) of the brake operating member and which is expected to be established by reduction of the effective diameter of the pressurizing piston, it indicates that the first control valve device and the master cylinder are both normal. If the master cylinder pressure cannot be increased to the above-indicated level, it indicates that at least one of the first control valve device and the master cylinder is defective or abnormal.
Where the braking pressure source device is operated without an operation of the brake operating member, the first control valve device and the master cylinder are diagnosed to be normal if the master cylinder pressure can be increased to a level which is expected to be established based on the back pressure in the back-pressure chamber generated by the pressurized fluid delivered from the power-operated hydraulic pressure source to the back-pressure chamber, or based on the above-indicated back pressure and the pressure of the fluid in the pressurizing chamber generated by the pressurized fluid delivered from the power-operated hydraulic pressure source to the pressurizing chamber through the communication passage. If the master cylinder pressure cannot be increased to the above-indicated level, it indicates that at least one of the first control valve device and the master cylinder is defective.
The braking pressure source device according to the above mode (19) can be diagnosed while it is being operated. Further, the diagnosis effected while the vehicle is in a stationary state does not disturb the normal braking operation of the braking system during running of the vehicle.
(20) A braking pressure source device according to the above mode (19), wherein the second diagnosing portion commands the first control valve device to effect the fluid communication while a brake pedal as the brake operating member is not in operation, and determines that the braking pressure source device is defective if a degree of increase of the fluid pressure in the pressurizing chamber with an increase of an operating force of the brake pedal operated after the first control valve device is commanded to effect said fluid communication is smaller than a predetermined threshold.
In the braking pressure source device according to the above mode (20), the second diagnosing portion can diagnose the braking pressure source device where the electric system of the vehicle is turned on while the brake pedal is not in operation. In this condition, the pressuring and back-pressure chambers are communicated with each other while the brake pedal is not in operation, the fluid pressure in the pressurizing chamber must be increased at a nominal rate determined by an effect of the fluid communication between the two chambers, from the very beginning of the operation of the brake pedal, if the braking pressure source device is normal. Therefore, the braking pressure source device can be diagnosed on the basis of the degree of increase of the fluid pressure in the pressurizing chamber with an increase of the operating force of the brake pedal. The degree of increase of the fluid pressure may be a rate of increase of the fluid pressure or an amount of increase of the fluid pressure.
(21) A braking pressure source device according to the above mode (20), wherein the braking system includes a wheel brake for braking a wheel of the automotive vehicle, the wheel brake having a wheel brake cylinder connected to the master cylinder and operable with a pressurized fluid delivered from the master cylinder, the braking pressure source device further comprising a third control valve device operable to disconnect the wheel brake cylinder from the master cylinder,
and wherein the second diagnosing portion commands the third control valve device to disconnect the wheel brake cylinder from the master cylinder when the second diagnosing portion commands the first control valve device to effect the fluid communication.
Like the first and second control valve devices, the third control valve device may be principally constituted by a solenoid-operated shut-off valve or a solenoid0operaetd pressure control valve.
The third control valve device may be provided for each of a plurality of wheel brake cylinders provided in the braking system. In this case, at least one or all of the third control valve devices corresponding to the respective wheel brake cylinders may be commanded to disconnect the corresponding wheel brake cylinder or cylinders from the master cylinder.
With the wheel brake cylinder being disconnected from the master cylinder by the third control valve device, the amount of flow of the pressurized fluid from the pressurizing chamber is zeroed or reduce. Accordingly, the amount of increase of the operating stroke of the brake pedal due to the fluid communication between the pressurizing and back-pressure chambers is reduced, making it possible to reduce a possibility of the vehicle operator feeling uneasy with the increase of the operating stroke. Where the diagnosis is effected with all of the wheel brake cylinders being disconnected from the master cylinder by the respective third control valve devices, the diagnosis does not disturb the normal braking operation of the braking system, since the diagnosis is effected in the stationary state of the vehicle. In this case, the vehicle operator is less likely to feel uneasy with an increase of the operating stroke of the brake pedal.
(22) A braking pressure source device according to the above mode (21), wherein the master cylinder is a tandem type master cylinder having two mutually independent pressurizing chambers, and the braking system has at least one first wheel brake cylinder connected to one of the two pressurizing chambers, and at least one second wheel brake cylinder connected to the other of the two pressurizing chambers, the third control valve device is disposed between the above-indicated one pressurizing chamber and the above-indicated at least one first wheel brake cylinder.
When the braking pressure source device is diagnosed, the above-indicated one of the two pressurizing chambers of the master cylinder and the at least one first wheel brake cylinder are disconnected from each other, while the other pressurizing chamber and the above-indicated at least one second wheel brake cylinder are communicated with each other. Accordingly, the diagnosis is effected while the stationary automotive vehicle is braked with the at least one second wheel brake cylinder, with a reduced amount of flow of the fluid from the master cylinder, which reduces a possibility of the vehicle operator feeling uneasy with an increase of the brake pedal operating stroke.
(23) A braking pressure source device according to the above mode (22), wherein the above-indicated at least one first wheel brake cylinder is at least one rear wheel brake cylinder for braking at least one rear wheel of the automotive vehicle.
In a braking system for an automotive vehicle, the front wheel brake generally has a large braking capacity than the rear wheel brake. In this braking system, the vehicle can be braked with a larger braking force by the front wheel brake with the front wheel brake cylinder in communicated with the master cylinder while the diagnosis is effected.
(24) A braking pressure source device according to any one of the above modes (20)-(23), wherein the second diagnosing portion determines that the braking pressure source device is defective, if the pressure of the fluid in the pressurizing chamber when the operating force of the brake pedal has exceeded a predetermined threshold is lower than a predetermined threshold.
The threshold of the fluid pressure in the pressurizing chamber is determined such that the fluid pressure in the pressurizing chamber exceeds the threshold when the operating force of the brake pedal has exceeded the threshold, if the braking pressure source device is normal. If the diagnosis is effected without depending upon the operating force of the brake pedal, it is not possible to determine whether the fluid pressure in the pressurizing chamber is lower than the threshold, because the operating force of the brake pedal is small, or because the braking pressure source device is defective. In the braking pressure source device according to the above mode (24), the second diagnosing portion determines whether the fluid pressure when the operating force has exceeded the threshold is smaller than the threshold. This fluid pressure should not be lower than the threshold if the braking pressure source device is normal, and therefore the braking pressure source device can be diagnosed to be defective, if the fluid pressure detected when the operating force has exceeded the threshold is lower than the threshold.
(25) A braking pressure source device according to any one of the above modes (20)-(24), wherein the second diagnosing portion determines that the braking pressure source device is defective, if a ratio of a rate of increase of the pressure of the fluid in the pressurizing chamber to a rate of increase of the operating force of the brake pedal is lower than a predetermined threshold.
The rate of increase of the fluid pressure in the pressurizing chamber and the rate of increase of the operating force of the brake pedal may be represented by amounts of increase of the fluid pressure and the operating force within a predetermined time, for instance, a cycle time of a diagnostic routine executed by the second diagnosing portion.
The rate of increase of the fluid pressure in the pressurizing chamber when the operating force of the brake pedal is increased at a given rate is higher when the pressurizing chamber is communicated with the back-pressure chamber to reduce the effective diameter of the pressurizing piston, than when the pressurizing chamber is not communicated with the back-pressure chamber. Therefore, the ratio of the rate of increase of the fluid pressure to the rate of increase of the operating force is not lower than the predetermined threshold if the braking pressure source device is normal. In other words, the braking pressure source device can be diagnosed to be defective if the above-indicated ratio is lower than the threshold.
(26) A braking pressure source device according to the above mode (19), wherein the second diagnosing portion commands the first control valve device to effect the fluid communication between the pressurizing chamber and the back-pressure chamber while a brake pedal as the brake operating member is in operation, and determines that the braking pressure source device is defective, if a degree of increase of the fluid pressure in the pressurizing chamber after the first control valve device is commanded to effect the fluid communication is smaller than a predetermined threshold.
The braking pressure source device according to the above mode (26) can be diagnosed where the electric system of the braking system is turned on while the brake pedal is in operation. The fluid pressure in the pressurizing chamber must be increased after the first control valve device is commanded to effect the fluid communication between the pressurizing and back-pressure chambers, if the braking pressure source device is normal. The braking source device can be diagnosed to be defective, if the degree of increase of the fluid pressure is lower than the predetermined threshold after the two chambers are communicated with each other.
(27) A braking pressure source device according to the above mode (26), wherein the second diagnosing portion determines that the braking pressure source device is defective, if the degree of increase of the fluid pressure is not equal to or larger than the predetermined threshold within a predetermined time after the first valve device is commanded to effect the fluid communication
The operating state of the braking pressure source device as established when the pressurizing and back-pressure chambers are communicated with each other is not necessarily maintained for a long time. Further, the fluid communication between the two chambers is not necessarily completed immediately after the first control valve device is commanded to effect the fluid communication. In view of these possibilities, the predetermined time indicated above is determined to be longer than the time required for completing the fluid communication between the two chambers, and such that the operating state of the braking pressure source device is not likely to change within the predetermined time, for instance, such that the brake pedal is not likely to be released within the predetermined time. In the braking pressure source device according to the above mode (27), the second diagnosing portion assures an accurate diagnosis of the braking pressure source device while the pressurizing and back-pressure chambers are held in communication with each other, and without an influence of a change in the operating state of the braking pressure source device.
(28) A braking pressure source device according to the above mode (26) or (27), wherein the second diagnosing portion commands the first control valve device to effect the fluid communication while the operating force of the brake pedal is held substantially constant.
Although the diagnosis may be effected while the brake pedal is being depressed, the diagnosis is preferably effected while the brake pedal is kept in substantially the same operated position or while the operating force of the brake pedal is held substantially constant. In this respect, the second diagnosing portion preferably includes a constant-brake-operating-force detecting portion operable to detect that the operating force of the brake pedal is held substantially constant within a predetermined time, and a commanding portion operable upon detecting of this condition by the detecting portion, to command the first control valve device to effect the fluid communication between the two chambers. This arrangement permits accurate detection of the increase of the fluid pressure in the pressurizing chamber due to the fluid communication, without an influence of an increase in the operating force of the brake pedal, and assures an accurate diagnosis of the braking pressure source device.
(29) A braking pressure source device according to any one of the above modes (26)-(28), wherein the braking system includes a wheel brake for braking a wheel of the automotive vehicle, the wheel brake having a wheel brake cylinder connected to the master cylinder and operable with a pressurized fluid delivered from the master cylinder, the braking pressure source device further comprising a third control valve device operable to disconnect the wheel brake cylinder from the master cylinder, and wherein the second diagnosing portion commands the third control valve device to disconnect the wheel brake cylinder from the master cylinder when the second diagnosing portion commands the first control valve device to effect the fluid communication.
In the braking pressure source device according to the above mode (29), the pressurized fluid is not delivered from the master cylinder to the wheel brake cylinder during the diagnosis, since the wheel brake cylinder is held disconnected from the master cylinder by the third control valve device while the pressurizing and back-pressure chambers are held in communication with each other. Accordingly, the operating stroke of the brake pedal is not increased, so that if the braking pressure source device is normal, the operating force of the brake pedal becomes equal to or higher than the value when the first control valve device was command to effect fluid communication between the two chambers. Therefore, the fluid pressure in the pressurizing chamber is increased by at least an amount corresponding to an effect of the fluid communication. The present arrangement assures improved accuracy of diagnosis of the braking pressure source device on the basis of the degree of increase of the fluid pressure in the pressurizing chamber.
The operating stroke of the brake pedal is not increased since the wheel brake cylinder is disconnected from the master cylinder by the third control valve device and since the operating force of the brake pedal is held substantially constant while the pressurizing and back-pressure chambers are held in communication with each other. Accordingly, the fluid pressure in the pressurizing chamber is increased to a level corresponding to the operating force of the brake pedal, after the fluid communication between the two chambers is completed. That is, the effect of the fluid communication can be accurately reflected on the increase of the fluid pressure in the pressurizing chamber, in the above-indicated condition, so that the braking pressure source device can be diagnosed with high reliability, depending upon the degree of increase of the fluid pressure in the pressurizing chamber. Further, the present arrangement is free from the vehicle operator""s recognition of the diagnosis, since the diagnosis is effected while the operating force of the brake pedal is held substantially constant by the vehicle operator. If the diagnosis were effected during a vehicle operator""s effort to depress the brake pedal while the master cylinder and the wheel brake cylinders are disconnected from each other, the vehicle operator would feel uneasy with the brake pedal which cannot be depressed in the normal manner.
If the vehicle operator tries to depress the brake pedal after the third control valve device is commanded to disconnect the master cylinder and the wheel brake cylinder from each other, the vehicle operator feels uneasy with difficulty in depressing the brake pedal. In this case, the operating force of the brake pedal is usually increased, and the fluid pressure in the pressurizing chamber in relation to the brake pedal operating force is eventually stabilized when the fluid communication between the pressurizing and back-pressure chambers is completed. In this case, too, therefore, the braking pressure source device can be diagnosed with high reliability depending upon the degree of increase of the fluid pressure in the pressurizing chamber.
It is not essential to disconnect the wheel brake cylinder from the master cylinder during the diagnosis. Where the third control valve device is not provided, or when the third control valve device is placed in a state in which the master cylinder and the wheel brake cylinder are held in communication with each other, the brake pedal can be depressed with the pressurized fluid being delivered from the master cylinder to the wheel brake cylinder, and the operating force of the brake pedal may possibly be reduced due to a decrease in the reaction force transmitted from the master cylinder to the brake pedal upon fluid communication between the pressurizing and back-pressure chambers. Thus, the state in which the fluid pressure in the pressurizing chamber is increased upon fluid communication between the two chambers is likely to vary if the wheel brake cylinder is disconnected from the master cylinder during the diagnosis. In the braking pressure source device according to the above mode (29), however, the diagnosis is effected while the master cylinder and the wheel brake cylinder are held disconnected from each other, so that the braking pressure source device can be diagnosed with high reliability on the basis of the master cylinder pressure accurately detected during the fluid communication between the pressurizing and back-pressure chambers.
(30) A braking pressure source device according to any one of the above modes (26)-(30), wherein the master cylinder is a tandem type master cylinder having two mutually independent pressurizing chambers, and the braking system has at least one first wheel brake cylinder connected to one of the two pressurizing chambers, and at least one second wheel brake cylinder connected to the other of the two pressurizing chambers, the third control valve device is disposed between each of the two pressurizing chambers and the at least one wheel brake cylinder connected thereto.
In the braking pressure source device according to the above mode (30), the first control valve device is commanded to effect the fluid communication between the pressurizing and back-pressure chambers while the brake pedal is in operation, and the diagnosis is effected during an operation of the brake pedal, that is, after the brake pedal has been operated to activate the wheel brake cylinders. In this state, the vehicle is braked with the wheel brake cylinders even if all of the wheel brake cylinders are disconnected from the master cylinder during the diagnosis. Since the pressurized fluid is not delivered from the pressurizing chamber to the wheel brake cylinders during the diagnosis, the operating stroke of the brake pedal is not increased when the pressurizing and back-pressure chambers are communicated with each other, so that the vehicle operator will not feel uneasy with an increase of the brake pedal operating stroke which would take place if the wheel brake cylinders were not disconnected from the master cylinder.
(31) A braking pressure source device according to any one of the above modes (26)-(30), wherein the second diagnosing portion determines that the braking pressure source device is defective, if a ratio of an operating force of the brake pedal to the fluid pressure in said pressurizing chamber is higher than a predetermined positive threshold valve.
If the master cylinder and the wheel brake cylinder are disconnected from each other by the third control valve device and the operating force of the brake pedal is held substantially constant when the pressurizing and back-pressure chambers are communicated with each other, the fluid pressure in the pressurizing chamber (master cylinder pressure) is increased due to the fluid communication between the two chambers (owing to an effect of the effective diameter of the pressurizing piston). Since the brake pedal operating force is substantially constant, the ratio of the brake pedal operating force to the master cylinder pressure is comparatively low (positive value).
If the third control valve device is not provided or if the master cylinder and the wheel brake cylinder are not disconnected by the third control valve device when the pressurizing and back-pressure chambers are communicated with each other, the reaction force transmitted from the master cylinder to the brake pedal is rapidly reduced, so that the operating stroke of the brake pedal is increased (due to the pedal sink), and the operating force acting on the brake pedal is reduced. If the brake pedal is not further depressed by the vehicle operator in this state, the operating force of the brake pedal remains at the reduced value. Usually, the vehicle operator further depresses the brake pedal in an attempt to restore the previous operating force, so that the master cylinder pressure is eventually increased as a result of the fluid communication between the pressurizing and back-pressure chambers, so that the ratio of the brake pedal operating force to the master cylinder pressure is a comparatively small value. Even if the brake pedal operating force remains at the reduced value without a further depression of the brake pedal by the vehicle operator, the relationship between the operating force and the master cylinder pressure is the nominal relationship to be established when the effective diameter of the pressurizing piston is reduced as a result of the fluid communication. In this case, too, the ratio of the operating force to the increased master cylinder pressure is a comparatively small positive value. Where the pressurizing and back-pressure chambers are communicated with each other while the brake pedal is being depressed, the amount of increase of the operating stroke of the brake pedal as felt by the vehicle operator is not so large. In this respect, it is noted that the fluid communication between the pressurizing and back-pressure chambers is not completed immediately after the first control valve device is commanded to effect the fluid communication, so that the master cylinder pressure is increased at a relatively low rate due to the fluid communication, and therefore the reaction force indicated above is only slowly reduced with a result of a slow increase of the brake pedal operating stroke. Accordingly, the vehicle operator is less likely to feel uneasy with an increase of the operating stroke.
As described above, the ratio of the operating force of the brake pedal to the master cylinder pressure is a comparatively small value even in the absence of the third control valve device, even while the operating force of the brake pedal is held constant, or even if the diagnosis is effected during depression of the brake pedal, provided the braking pressure source device is normal. Thus, the braking pressure source device can be diagnosed depending upon whether the above-indicated ratio is larger than the predetermined threshold or not.
(32) A braking pressure source device according to any one of the above modes (28)-(30), wherein the second diagnosing portion determines that the braking pressure source device is defective, if a rate of increase of the fluid pressure in the pressurizing chamber is lower than a predetermined threshold.
The rate of increase of the fluid pressure in the pressurizing chamber may be represented by an amount of increase of the fluid pressure within a predetermined time, for instance, a cycle time of a diagnostic routine executed by the second diagnosing portion.
If the braking pressure source device is normal, the rate of increase of the fluid pressure in the pressurizing chamber (master cylinder pressure) as a result of reduction of the effective diameter of the pressurizing piston upon fluid communication between the pressurizing and back-pressure chambers is not lower than the predetermined threshold. The operating force and stroke of the brake pedal will not change as a result of the reduction of the effective diameter of the pressurizing piston, since the operating force is held substantially constant, if the master cylinder and the wheel brake cylinder are disconnected from each other by the third control valve device. Accordingly, the master cylinder pressure is increased at a rate not lower than the threshold value, when the pressurizing and back-pressure chambers are communicated with each other. Therefore, the braking pressure source device can be diagnosed on the basis of the rate of increase of the master cylinder pressure.
If the third control valve device is not provided or if the master cylinder and the wheel brake cylinder are not disconnected by the third control valve device when the pressurizing and back-pressure chambers are communicated with each other, the reaction force transmitted from the master cylinder to the brake pedal is rapidly reduced, so that the operating stroke of the brake pedal is increased (due to the pedal sink), and the operating force acting on the brake pedal is reduced. Usually, the vehicle operator further depresses the brake pedal in an attempt to restore the previous operating force, so that the master cylinder pressure is eventually increased as a result of the fluid communication between the pressurizing and back-pressure chambers, so that the braking pressure source device can be diagnosed on the basis of the rate of increase of the master cylinder pressure. This rate of increase of the master cylinder pressure changes with a change in the speed at which the brake pedal is depressed by the vehicle operator. The above-indicated threshold value of the rate of increase is determined to permit the diagnosis even when the operating speed of the brake pedal is comparatively low and the rate of increase of the master cylinder pressure is accordingly low. Where the third control valve device is provided to disconnect the master cylinder and the wheel brake cylinder from each other, the master cylinder pressure is increased at a rate irrespective of the operating speed of the brake pedal, so that the effect of the reduction of the effective diameter of the pressurizing piston can be accurately reflected on the rate of increase of the master cylinder pressure. Accordingly, the braking pressure source device can be diagnosed with high reliability.
The master cylinder pressure is increased in the process of the fluid communication between the pressurizing and back-pressure chamber, but is not increased after the fluid communication is completed, and the rate of increase of the master cylinder pressure will not be equal to or higher than the threshold, except where the brake pedal can be further depressed with an increased operating force in the absence of the third control valve device or when the master cylinder and the wheel brake cylinder are not disconnected from each other by the third control valve device. In view of the above, the determination as to whether the rate of increase of the master cylinder pressure is lower than the threshold is desirably effected within a predetermined time after the first control valve device is commanded to effect the fluid communication, namely, at a point of time relatively close to the moment at which the fluid communication (reduction of the effective diameter of the pressurizing piston ) is completed.
(33) A braking pressure source device according to any one of the above modes (19)-(32), wherein the braking system includes a wheel brake for braking a wheel of the automotive vehicle, the wheel brake having a wheel brake cylinder connected to the master cylinder and operable with a pressurized fluid delivered from the master cylinder, the braking pressure source device further comprising a third control valve device operable to disconnect the wheel brake cylinder from the master cylinder,
and wherein the second diagnosing portion commands the third control valve device to connect the wheel brake cylinder to the master cylinder when the operating force of the brake operating member has exceeded a predetermined threshold, and/or when a movement of the automotive vehicle is initiated.
The automotive vehicle is moved by operation of an engine, for instance, or moved down on a downhill by gravity without an operation of the engine.
When the operating force of the brake operating member has exceeded the threshold, it indicates that the vehicle operator intends to brake the vehicle with a relatively large braking force. When a movement of the vehicle is initiated, it indicates that the vehicle may be required to be braked at any time. Therefore, the third control valve device is commanded to connect the master cylinder and the wheel brake cylinder to each other, to brake the vehicle with an increased braking force when the operating force has exceeded the threshold, or to place the wheel brake cylinder in a state ready for operation when the brake operating member is operated.
(34) A braking pressure source device according to any one of the above modes (19)-(32), wherein the second diagnosing portion commands the first control valve device to disconnect the pressurizing and back-pressure chambers from each other when the operating force of the brake operating member has exceeded a predetermined threshold and/or when a movement of the automotive vehicle is initiated.
While the pressurizing and back-pressure chambers are disconnected from each other by the first control valve device, the braking pressure source device or the wheel brake is operated in the normal braking mode wherein the wheel brake cylinder is operated with the fluid pressurized in the pressurizing chamber based on only the braking force of the brake operating member, without depending on an effect of the fluid communication between the pressurizing and back-pressure chambers. Therefore, the wheel brake is operated in the normal braking mode when the brake operating member is operated with the operating force larger than the threshold, or when the brake operating member is operated after the movement of the vehicle is initiated. Thus, the diagnosis is interrupted with the first control valve device being restored to the state before the diagnosis, when the operating force of the brake operating member has exceeded the threshold and/or when the vehicle is moved.
(35) A braking pressure source device according to any one of the above modes (19)-(34), wherein the second diagnosing portion commands the first control valve device which has been held in a state for the above-indicated fluid communication, to be placed in s state for disconnecting the pressurizing and back-pressure chambers from each other, when the brake operating member is returned to a non-operated position thereof.
In the braking pressure source device according to the above mode (35), the pressurizing and back-pressure chambers are disconnected from each other by the first control valve device, when the brake operating member is returned to its non-operated position, irrespective of whether the diagnosis is terminated or not. Where the first control valve device is normally placed in the closed state for disconnecting the pressurizing and back-pressure chambers, this first control valve device is returned to the normally established closed state in which the braking pressure source device is operated in the normal braking mode. If the diagnosis is not terminated before the brake operating member is returned to the non-operated position, the diagnosis is terminated when the brake operating member is returned to the non-operated position.
(36) A braking pressure source device according to any one of the above modes (20)-(35), wherein the braking system includes a wheel brake for braking a wheel of the automotive vehicle, the wheel brake having a wheel brake cylinder connected to the master cylinder and operable with a pressurized fluid delivered from the master cylinder, the braking pressure source device further comprising a third control valve device operable to disconnect the wheel brake cylinder from the master cylinder,
and wherein the second diagnosing portion commands the to third control valve device which has been held in s state for disconnecting the wheel brake cylinder from the master cylinder, to be placed in a state for communication between the wheel brake cylinder and the master cylinder, when the brake operating member is returned to a non-operated position thereof.
In the braking pressure source device according to the above mode (36), the wheel brake cylinder and the master cylinder are communicated with each other through the third control valve device, when the brake operating member is returned to its non-operated position, irrespective of whether the diagnosis is terminated or not. Thus, the wheel brake cylinder is made ready for operation when the brake operating member is subsequently operated. If the diagnosis is not terminated before the brake operating member is returned to the non-operated position, the diagnosis is terminated when the brake operating member is returned to the non-operated position.
(37) A braking pressure source device according to any one of the above modes (19)-(36), wherein the second diagnosing portion commands the first control valve device to disconnect the pressurizing and back-pressure chambers from each other when the second diagnosing portion determines that the braking pressure source device is defective.
In the braking pressure source device, the pressurizing and back-pressure chambers are disconnected from each other when the braking pressure source device is diagnosed to be defective. It is possible to hold the first control valve device in a state for disconnection of the pressurizing and back-pressure chambers, until the defect is eliminated.
(38) A braking pressure source device according to any one of the above modes (20)-(37), wherein the braking system includes a wheel brake for braking a wheel of the automotive vehicle, the wheel brake having a wheel brake cylinder connected to the master cylinder and operable with a pressurized fluid delivered from the master cylinder, the braking pressure source device further comprising a third control valve device operable to disconnect the wheel brake cylinder from the master cylinder,
and wherein the second diagnosing portion commands the third control valve device to be placed in a state for fluid communication between the wheel brake cylinder and the master cylinder, when the second diagnosing portion determines that the braking pressure source device is defective.
In the braking pressure source device according to the above mode (38), the wheel brake cylinder and the master cylinder are communicated with each other through the third control valve device, when the braking pressure source device is diagnosed to be defective.
(39) A braking pressure source device according to any one of the above modes (1)-(38), further comprising a power-operated hydraulic pressure source including a pump and a drive device for operating the pump to deliver a pressurized fluid to the back-pressure chamber.
(40) A braking pressure source device according to the above mode (39), further comprising a pressure control valve device disposed between the power-operated hydraulic pressure source and the back-pressure chamber, the pressure control valve device controlling a pressure of a pressurized fluid delivered from the power-operated hydraulic pressure source to the back-pressure chamber.
(41) A braking pressure source device according to the above mode (40), wherein the pressure control valve device includes a reservoir, a pressure-increasing valve for effecting fluid communication between the power-operated hydraulic pressure source and the back-pressure chamber to increase the pressure of the fluid in the back-pressure chamber, and a pressure-reducing valve for permitting the pressurized fluid to be discharged from the back-pressure chamber to the reservoir to reduce the pressure of the fluid in the back-pressure chamber.
(42 A braking pressure source device according to the above mode (41), wherein at least one of the pressure-increasing and pressure-reducing valves is a linear solenoid valve capable of continuously changing the pressure of the fluid in the back-pressure chamber with a change in an amount of electric power applied thereto.
(43) A braking pressure source device according to any one of the above modes (39)-(42), wherein the power-operated hydraulic pressure source further includes an accumulator for storing the pressurized fluid delivered from the pump.
(44) A braking pressure source device according to any one of the above modes (39)-(42), wherein the drive device of the power-operated hydraulic pressure source is an electric motor for operating the pump, the braking pressure source device further comprising a motor controller for controlling an amount of electric power to be applied to the electric motor to control at least one of a delivery pressure and a delivery rate of the pump.